Clamping device and printer

ABSTRACT

A sheet  3  is caught between a clamper  15  and a platen drum  10  at its sheet front end portion. The clamper  15  is provided with a pressing member  32  with elasticity, and the pressing member  32  has two projections  32   b.  During conveyance, a pressing surface  32   a  tightly comes into contact with the front end portion of the sheet  3,  while each projection  32   b  is elastically deformed and compressed. When correcting skew of the sheet  3,  the clamper  15  is turned, while only the projections  32   b  press the front end portion of the sheet  3.

TECHNICAL FIELD

The present invention relates to a clamping device for correcting skew of a lenticular sheet, and a printer for printing an image on the lenticular sheet.

BACKGROUND ART

Lenticular 3D photography in which a 3D image is observed with naked eyes with use of a lenticular sheet having a lot of lenses in an approximately semi-cylindrical shape arranged side by side is widely known. In the lenticular 3D photography, for example, each of an R viewpoint image and an L viewpoint image captured from two viewpoints of right and left is split into narrow stripes (lines), and the stripe images of the R viewpoint image and the stripe images of the L viewpoint image are alternately disposed on a back surface of the lenticular sheet, so as to locate the two adjoining stripe images under the single lens. Since the right and left eyes see through each lens the R and L viewpoint images with parallax, respectively, the 3D image is realized. It is also known that an N (N is three or more) number of viewpoint images are captured and split into narrow stripes, and an N number of stripe images are arranged behind the single lens to further improve a stereoscopic effect.

There are two types of lenticular 3D photography, including the type of overlaying the lenticular sheet on a sheet on which the stripe images are printed, and the type of printing the stripe images on a back surface of the lenticular sheet. In the case of printing the stripe images on the back surface of the lenticular sheet by using a printer, the lenticular sheet is intermittently conveyed in a sub scan direction. Just after each intermittent conveyance, a print head is actuated to print the stripe images extending in a main scan direction on the back surface of the lenticular lens one by one. Thus, at least the two kinds of viewpoint images having parallax are printed on the back surface of the lenticular sheet (refer to patent documents 1 and 2).

There is known a printer in which the stripe images are printed on a sheet and then this sheet is glued on the lenticular sheet (refer to patent document 3). This printer requires a mechanism for correctly positioning the lenticular sheet relative to the stripe images and gluing the sheets. For this reason, the printer of the type of printing the stripe images directly on the back surface of the lenticular lens has size and cost advantages.

By the way, when the plural viewpoint images are printed on the back surface of the lenticular sheet, the lenticular sheet is sometimes conveyed with inclination. This inclination is called skew. In this case, since the stripe images are printed in such a state that a longitudinal direction of the lens does not coincide with the main scan direction, print quality significantly deteriorates. In order to prevent the deterioration of the print quality caused by the skew of the lenticular sheet, various techniques are conventionally devised.

Patent document 1 describes a printer in which an optical sensor provided in the vicinity of a print head detects the position of the lenses, and the print position of the stripe images is adjusted based on a position detection result. Even if the lenticular sheet is skewed, the print position of the stripe images can be adjusted in accordance with the skew.

Patent document 2 describes a printer for correcting the skew of the lenticular sheet in advance. In this printer, an inclination angle of the longitudinal direction of the lens with respect to the main scan direction is detected. A conveyance amount in the sub scan direction is made different between right and left sides in accordance with a detection result, so that the lenticular sheet is turned around an axis orthogonal to its conveyance surface to correct the skew.

On the other hand, there are known two conveyance types of the printer, a linear conveyance type and a platen drum type. When printing a color image, for example, in the former type, a print sheet is conveyed on a linear conveyance path, and the color image is printed by a color sequential method during this reciprocating conveyance. In the latter type, the platen drum on which the print sheet is wound is rotated, and the color image is printed while the print sheet is conveyed in a rotation direction of the platen drum (refer to paten document 4, for example) . In the former type, since evacuation space of the print sheet is required before and behind the print head, the printer tends to be large in size. In the latter type, on the other hand, no evacuation space is required, and the print head and a sheet ejecting mechanism can be laid out around the platen drum, so this type of printer has an advantage in size reduction.

PRIOR ART DOCUMENTS Patent Documents

Patent document 1: Japanese Patent Laid-Open Publication No. 2007-76084 Patent document 2: Japanese Patent Laid-Open Publication No. 8-137034 Patent document 3: Japanese Patent Laid-Open Publication No. 7-219084 Patent document 4: Japanese Patent Laid-Open Publication No. 61-128677

SUMMARY OF INVENTION Problems to be Solved by the Invention

By the way, in the case of adjusting the print position of the stripe image, as described in the patent document 1, there is a problem that if the skew of the lenticular sheet is large, distortion of the viewpoint image printed on the reticular sheet becomes large, and causes deterioration in print quality. The printer for printing the stripe images on the lenticular sheet can get the size advantage by adopting the platen drum type. However, since the conveyance amount cannot be made different between the right and left sides, in contrast to the patent document 2, the skew of the lenticular sheet cannot be corrected. Furthermore, if the platen drum is turned around an axis orthogonal to its rotation axis with the aim of correcting the skew of the lenticular sheet, the distance between the print head and the platen drum becomes uneven. This causes deterioration in image quality.

A main object of the present invention is to provide a clamping device and a printer that can suitably correct skew of a lenticular sheet without causing image distortion. Another object of the present invention is to provide the printer that has simple structure and small size.

Means for Solving the Problems

A clamping device according to the present invention includes a clamper, a clamper shifting mechanism, a clamper turning mechanism, and a controller. The clamper has a pressing member with elasticity, and catches a part of a lenticular sheet between this pressing member and a support member. The support member supports at least a part of the lenticular sheet. The clamper shifting mechanism shifts the clamper among a retracted position, a first catching position, and a second catching position. In the retracted position, the pressing member is away from the support member. In the first catching position, the pressing member presses the part of the lenticular sheet so as to prevent a slip of the lenticular sheet from the pressing member and the support member. In the second catching position, the pressing member presses the part of the lenticular sheet so as to prevent a slip of the lenticular sheet from the pressing member and allow a slip of the lenticular sheet from the support member. The clamper turning mechanism turns the clamper around a turning axis orthogonal to the lenticular sheet. To turn the caught lenticular sheet, the controller controls the clamper shifting mechanism and the clamper turning mechanism so as to turn the clamper set in the second catching position. To fix the lenticular sheet on the support member, the controller controls the clamper shifting mechanism so as to set the clamper in the first catching position.

The pressing member preferably has a plurality of projections formed in a pressing surface faced to the support member. In the first catching position, the pressing surface is pressed against the part of the lenticular sheet while compressing each projection, so the part of the lenticular sheet is caught between the pressing surface and the support member. In the second catching position, each projection is pressed against the part of the lenticular sheet with a compression value of each projection lower than that of the first catching position, so the part of the lenticular sheet is caught between each projection and the support member.

The size of the projection is preferably in accordance with a distance from the turning axis. In the second catching position, an area at which the projection contacts with the lenticular sheet preferably differs in accordance with the distance from the turning axis.

It is preferable that out of a surface area of the support member, at least an area faced to each projection plus a movable area of each projection by the clamper turning mechanism are allocated to a non-formation area, and a remaining area is allocated to a formation area, and an elastic layer having elasticity is formed in the formation area to make a coefficient of friction in the non-formation area smaller than that in the formation area.

The formation area preferably includes a portion of the support member faced to the pressing surface, such that the part of the lenticular sheet is caught between the pressing surface and the elastic layer when the clamper is in the first catching position.

A printer according to the present invention, which conveys in a sub scan direction a lenticular sheet having a plurality of lenses formed in a front surface of the lenticular sheet and sequentially prints on a back surface of the lenticular sheet a plurality of stripe images parallel to a main scan direction orthogonal to the sub scan direction, includes a platen, a clamper, a clamper shifting mechanism, a skew detection section, a clamper turning mechanism, and a controller. The platen supports the lenticular sheet and moves the lenticular sheet in the sub scan direction. The clamper has a pressing member with elasticity, and presses a sheet end portion of the lenticular sheet against the platen to catch the sheet end portion between the clamper itself and the platen. The clamper shifting mechanism shifts the clamper among a retracted position, a first catching position, and a second catching position. In the retracted position, the pressing member is away from the platen. In the first catching position, the pressing member presses the sheet end portion of the lenticular sheet so as to prevent a slip of the lenticular sheet from the pressing member and the platen. In the second catching position, the pressing member presses the sheet end portion of the lenticular sheet so as to prevent a slip of the lenticular sheet from the pressing member and allow a slip of the lenticular sheet from the platen. The skew detection section detects skew of the lenticular sheet. The clamper turning mechanism turns the clamper around a turning axis orthogonal to the lenticular sheet. To correct the skew of the lenticular sheet with respect to the main scan direction, the controller controls the clamper shifting mechanism and the clamper turning mechanism to turn the clamper set in the second catching position based on a detection result of the skew detection section. To convey the lenticular sheet in the sub scan direction, the controller controls the clamper shifting mechanism and sets the clamper in the first catching position while the platen is moved in the sub scan direction.

The pressing member preferably has a plurality of projections formed in a pressing surface faced to the platen. In the first catching position, the pressing surface is pressed against the sheet end portion while compressing each projection, to catch the sheet end portion between the pressing surface and the platen. In the second catching position, each projection is pressed against the sheet end portion with a compression value lower than that of the first catching position, to catch the sheet end portion between each projection and the platen.

The size of the projection is preferably in accordance with a distance from the turning axis. In the second catching position, an area at which the projection contacts with the lenticular sheet preferably differs in accordance with the distance from the turning axis.

Out of a surface area of the platen, at least an area faced to each projection plus a movable area of each projection by the clamper turning mechanism are preferably allocated to a non-formation area, while a remaining area is preferably allocated to a formation area. It is preferable that an elastic layer having elasticity is formed in the formation area, and a coefficient of friction is smaller in the non-formation area than that in the formation area.

The formation area preferably includes a portion of the platen faced to the pressing surface, such that the sheet end portion is caught between the pressing surface and the elastic layer, when the clamper is in the first catching position.

The platen is preferably a rotatable platen drum on which the lenticular sheet is wound.

A sheet front end portion of the lenticular sheet is preferably caught between the clamper and the platen.

Effect of the Invention

According to the present invention, it is possible to correct the skew of the lenticular sheet with simple structure. Also, printing is carried out with contributing to simplified structure and reduced size without occurrence of deterioration in image quality, such as distortion of an image.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory view showing an outline of a printer to which the present invention is applied.

FIG. 2 is a perspective view of a lenticular sheet.

FIG. 3 is an explanatory view showing a state of peeling the lenticular sheet by a peeling claw.

FIG. 4 is a perspective view showing a bottom side of a clamper;

FIG. 5A is an explanatory view showing a state of the clamper in a retracted position.

FIG. 5B is an explanatory view showing a state of the clamper in a first catching position.

FIG. 5C is an explanatory view showing a state of the clamper in a second catching position.

FIG. 6 is an explanatory view of a platen drum showing an area having an elastic layer and an area without having the elastic layer.

FIG. 7 is an explanatory view showing the positional relation between a pressing surface and projections of the clamper and the area without having the elastic layer.

FIG. 8 is an explanatory view showing an arrangement of lens sensors relative to the lenticular sheet.

FIG. 9 is a perspective view of a clamper unit.

FIG. 10 is a perspective view showing a rear end clamp and an open/close mechanism thereof.

FIG. 11 is a flowchart showing a procedure from skew correction to printing.

FIG. 12 is an explanatory view of an embodiment in which only areas faced to the projections plus movable areas of the projections are allocated to non-formation areas of the elastic layer.

FIG. 13 is an explanatory view of another embodiment in which the projections are changed in size in accordance with distance from a turning axis of the clamper.

DESCRIPTION OF INVENTION

In FIG. 1, a printer 2 prints a parallax image (a collection of viewpoint images) for observing a 3D image on a back surface of a lenticular sheet (hereinafter simply called sheet) 3 by a sublimation method. This printer 2 converts two viewpoint images into six viewpoint images, and splits the six viewpoint images into many stripe images, and prints the stripe images on the sheet 3.

As shown in FIG. 2, many lenses 4 in the shape of an approximately cylinder (cylindrical) are arranged on the side of a front surface of the sheet 3, and the back surface of the sheet 3 is flat, as is well known. Each lens 4 extends in a main scan direction. The back surface of the sheet 3 is virtually partitioned into image areas 5 in accordance with the individual lenses 4, and the single image area 5 corresponds to the single lens 4. Each image area 5 is partitioned in an arrangement direction of the lenses 4 in accordance with the number of the viewpoint images.

In this embodiment, the image area 5 is partitioned into first to sixth small areas 5 a to 5 f. The stripe images, into which the six viewpoint images are split into stripes, are printed on the first to sixth small areas 5 a to 5 f. The small areas 5 a to 5 f correspond to the first to sixth viewpoint images on a one-by-one basis. In this embodiment, each of the small areas 5 a to 5 f has a width (length in a sub scan direction) of approximately 40 μm, and a single line has a width of approximately 20 μm. Thus, for example, two adjoining lines of the first viewpoint image are printed side by side on the first small area 5 a as the single stripe image.

As shown in FIG. 1, the printer 2 is provided with a paper feed cassette 9. The paper feed cassette 9 contains a stack of sheets 3. In printing, a paper feed mechanism (not shown) supplies the single sheet 3 from the paper feed cassette 9 to a feeding path 6. The sheet 3 is conveyed through the feeding path 6 with the lenses 4 facing down in the arrangement direction (sub scan direction) of the lenses 4. Note that, the sheet 3 may be manually inserted into the feeding path 6 instead.

In the feeding path 6, there are provided a feeding roller pair 7 and a sensor section 8 in this order from an upstream side (on the side of the paper feed cassette 9), and a platen drum 10 is disposed downstream from the feeding path 6. The feeding path 6 extends in a tangential direction of an outer circumference of the platen drum 10, so the sheet 3 supplied from the feeding path 6 is fed to an outer circumferential surface of the platen drum 10.

The feeding roller pair 7 is constituted of a capstan roller 7 a rotated by a motor 12, and a pinch roller 7 b that is shiftable between a nip position for nipping the sheet 3 between itself and the capstan roller 7 a and a release position being distant from the sheet 3. The feeding roller pair 7 nips the sheet and conveys the sheet 3 to the platen drum 10 by the rotation of the capstan roller 7 a.

The platen drum 10 is rotatably supported by a shaft 10 a parallel to the main scan direction, and rotated by a motor 14. The rotation direction of the motor 14 is changeable, and hence the platen drum 10 is rotated in one of a forward direction indicated by an arrow A and a reverse direction opposite thereto.

In printing, the sheet 3 is wound onto the outer circumferential surface 10 b of the platen drum 10. The platen drum 10 conveys the sheet 3 in the sub scan direction by its rotation. The sheet 3 is wound in such an orientation that the lenses 4 face to a platen drum side and the arrangement direction of the lenses 4 corresponds with a circumferential direction (sub scan direction) of the platen drum 10.

A clamper 15, a clamper shifting mechanism 16, and a clamper turning mechanism 17 compose a clamp unit. The clamper 15 catches a front end portion (hereinafter called sheet front end portion) of the sheet 3 between itself and the outer circumferential surface 10 b. The clamper 15 is integrated into the platen drum 10, and rotated integrally with the platen drum 10 to the sub scan direction. In this embodiment, the platen drum 10 functions as a support member. The platen drum 10 and the motor 14 compose a conveyance mechanism for conveying the sheet 3 in the sub scan direction.

The clamper shifting mechanism 16 shifts the clamper 15 in a radial direction of the platen drum 10. By the clamper shifting mechanism 16, the clamper 15 is shifted between a catching position for catching the sheet front end portion between itself and the outer circumferential surface 10 b and a retracted position for releasing the catch. The catching position includes a first catching position for tightly catching the sheet front end portion, and a second catching position for catching the sheet front end portion more loosely than that in the first catching position.

The clamper turning mechanism 17 turns the clamper 15 around a turning axis orthogonal to the surface of the sheet 3. The clamper 15 is turned while catching the sheet 3, so that the sheet 3 is turned by an arbitrary angle to correct its skew. In this embodiment, the radial direction of the platen drum 10 coincides with a direction orthogonal to the sheet 3 wound on the platen drum 10.

In the outer circumference of the platen drum 10, a thermal head 18 and a peeling claw 19 are disposed. The thermal head 18 has at its bottom two heating element arrays 18 a, each of which is composed of a lot of heating elements linearly arranged in the main scan direction. The provision of the two heating element arrays 18 a adjoining to each other makes it possible to print the single stripe image (two lines) at a time. Then, conveyance of the sheet 3 for six times in the sub scan direction by the width of the small area makes it possible to print the single image area 5. The length of each heating element array 18 a in the main scan direction is slightly longer than the width (length in the main scan direction) of a print area of the sheet 3.

The thermal head 18 is shifted between a pressing position for pressing a print film 21 against the back surface of the sheet 3 in a state of overlaying the print film 21 on the back surface of the sheet 3 on the platen drum 10 and a retracted position for retracting upward from the pressing position. The print film 21 includes an image receptor film, a yellow ink film, a magenta ink film, a cyan ink film, and a back layer film. The size of each film is approximately the same as that of the sheet 3. These films are joined side by side to compose a film set for the single sheet. The print film 21 is fed from one of spools to the other and wound up thereto, in synchronization with the conveyance of the sheet 3.

The image receptor film forms on the back surface of the sheet 3 an image receptor layer (under layer) that is stained with color ink from the ink films. When the image receptor film is heated by the thermal head 18 while being overlaid on the back surface of the sheet 3, the transparent image receptor layer is transferred to the back surface of the sheet 3.

The yellow, magenta, and cyan ink films are well known dye-sublimation ink films. When each ink film is heated by the thermal head 18 while being overlaid on the image receptor layer formed on the back surface of the sheet 3, the ink sublimates and is transferred to the image receptor layer. The amount of adhesion of the ink increases or decreases in accordance with a heating value of the thermal head 18, and this facilitates representation of a halftone. Note that, by using a black ink film, the printing with four colors may be carried out.

The back layer film transfers a white back layer to the image, when being heated by the thermal head 18 in a state of being overlaid on the image printed on the sheet 3. This back layer reflects light, and allows observation of the bright and sharp color 3D image.

A head driver 22 composes a printing section 23 together with the thermal head 18. The head driver 22 drives every heating element of the thermal head 18. In forming the image receptor layer and the back layer, the head driver 22 drives the thermal head 18 such that every heating element generates the same heating value. This heating value is set at a value necessary for transferring the image receptor layer and the back layer. In printing an image with use of the ink films, the head driver 22 prints a full color image by a three-color field sequential printing. In this case, each heating element is heated based on image data of the six viewpoint images, to obtain ink density corresponding to the image data.

The image data of the image to be printed is inputted to a controller 24. The inputted image data is the viewpoint images from two viewpoints, for example. The controller 24 converts the image data from the two viewpoints into image data from six viewpoints. The converted image data from six viewpoints is sent to the head driver 22.

The peeling claw 19 peels the printed sheet 3 from the platen drum 10, and guides the sheet 3 into a cutter unit 25. The peeling claw 19 is disposed in the middle of the sheet 3 in the width direction, and swingable between a retracted position in which a tip of the peeling claw 19 is away from the outer circumferential surface 10 b as shown in FIG. 1 and a peeling position in which the tip makes contact with the outer circumferential surface 10 b as shown in FIG. 3. When the platen drum 10 is rotated in the reverse direction in a state of setting the peeling claw 19 in the peeling position, the peeling claw 19 scoops the sheet from its rear end and guides the sheet 3 into the cutter unit 25. The cutter unit 25 cuts off margins, that is, the sheet front end portion and a rear end portion of the sheet 3 (hereinafter called sheet rear end portion) , which are caught by the clamper 15 and rear end clamps 27, respectively, and no image is printed thereto. Then, the cutter unit 25 ejects the cut sheet 3 from the printer.

Note that, the position of the peeling claw 19 is adjusted such that when the peeling claw 19 scoops the rear end of the sheet 3 by the reverse rotation of the platen drum 10 and the platen drum 10 is further rotated by a small amount in the reverse direction, the rotation position of the platen drum 10 is set in a standby position, as described later, for actuating the clamper 15. Thus, after releasing the catch of the sheet 3, a conveyance mechanism contained in the cutter unit 25 can convey the sheet 3.

On the outer circumference of the platen drum 10, a plurality of guide rollers 26 are disposed. When the sheet 3 is wound onto the platen drum 10, these guide rollers 26 are pressed against the platen drum 10 so as to catch the sheet 3 therebetween. Thus, until the rear end clamps 27 catch the sheet rear end portion, the guide rollers 26 prevent the sheet 3 from floating from the outer circumferential surface 10 b due to solidity of the sheet 3 itself. Note that, for example, the guide rollers 26 are shiftable in the radial direction of the platen drum 10, so the guide rollers 26 do not interfere with the moving clamper 15.

The rear end clamps 27 are operated by an open/close mechanism 28, and are shifted between a catching position for catching the sheet 3 and a retracted position for releasing the catch. The rear end clamps 27 catch the sheet rear end portion between themselves and the platen drum 10, in order to prevent the sheet 3 from floating from the outer circumferential surface 10 b due to the solidity of the sheet 3 itself during printing. These rear end clamps 27 are rotated integrally with the platen drum 10.

The controller 24 controls each part of the printer 2 including the motors 12 and 14, the peeling claw 19, the open/close mechanism 28, and the like in addition to the clamper shifting mechanism 16, the clamper turning mechanism 17, the head driver 22, and the like.

FIG. 4 shows the clamper 15 in such a posture that its bottom surface (side to face to the platen drum) faces upward. This clamper 15 is constituted of a base plate 31 having solidity and a pressing member 32 integrally provided on a lower surface of the base plate 31. The base plate 31, being a rectangular plate, has a length approximately the same as that of the sheet 3 in the main scan direction, and an appropriate width in the sub scan direction. The pressing member 32 has the same size as that of the base plate 31. In the pressing member 32, a pair of projections 32 b is formed in a flat pressing surface 32 a. The pressing member 32 is made of an elastic material having a high coefficient of friction. Such material includes rubber, for example. The projections 32 b are integrally formed of the same material as that of the pressing member 32, but may be formed of a material different from that of the pressing member 32 as long as the material has elasticity and a high coefficient of friction.

The protruding amount (height) of the projections 32 b is on the order of 0.1 to 0.3 mm. The distance between the pair of projections 32 b is set narrower than the width of the sheet 3, and the projections 32 b concurrently come into contact with the sheet 3. For convenience in explanation, each projection 32 b is exaggerated in FIG. 4 and other drawings.

As shown in FIG. 5A, in the retracted position, the clamper 15 makes an appropriate gap between the projections 32 b and the outer circumferential surface 10 b of the platen drum 10. This allows the sheet 3 fed from the feeding path 6 to get into space between the projections 32 b and the outer circumferential surface 10 b, and the sheet 3 to be pulled out of the space between the projections 32 b and the outer circumferential surface 10 b.

As shown in FIG. 5B, in the first catching position, the clamper 15 presses the sheet front end portion with the entire pressing surface 32 b. In this first catching position, each projection 32 b is pressed against the sheet front end portion, and elastically deformed and compressed. By catching the sheet front end portion with the entire pressing surface 32 a, as described above, the sheet front end portion is tightly caught without slipping off from the pressing member 32 and the outer circumferential surface 10 b. While the sheet 3 is conveyed, the clamper 15 is set in the first catching position.

As shown in FIG. 5C, in the second catching position, the clamper 15 is slightly shifted to the side of the retracted position, as compared to the first catching position. Thus, the pressing surface 32 a is away from the sheet 3, and each projection 32 b is compressed with a compression amount less than that of the first catching position. The sheet front end portion is pressed and caught only by the projections 32 b. This catching position allows the sheet front end portion to slip off from the outer circumferential surface 10 b, while prevents the sheet front end portion from slipping out of the projections 32 b. When correcting the skew of the sheet 3, the clamper 15 is set in the second catching position. When the clamper 15 is set in the second catching position and turned, the sheet 3 is turned by following the turn of the clamper 15.

As shown in FIG. 6, an elastic layer 35 having elasticity is formed on a surface of a drum body 34 made of metal, for example. This elastic layer 35 is provided with the aim of preventing a scratch on the sheet 3 caused by slipping by dint of tight contact with the sheet 3, improving contact of the thermal head 18 with the sheet 3, and the like. Such elastic layer 35 is formed by spray coating of the rubber, for example.

The formation of the elastic layer 35 as described above on the entire circumference of the platen drum 10 deteriorates a slip between the sheet front end portion and the elastic layer 35. Thus, even if the clamper 15 set in the second catching position is turned, the sheet 3 could not be turned with following the turn of the clamper 15 with precision.

Therefore, in the platen drum 10, a part of the outer circumferential surface 10 b is allocated to a non-formation area 36 in which no elastic layer 35 is formed, and the remaining part is allocated to a formation area 37 in which the elastic layer 35 is formed. The non-formation area 36 is situated in a portion facing to the clamper 15. From the non-formation area 36, the surface of the drum body 34, which has a lower coefficient of friction than that of the surface of the elastic layer 35, is exposed.

As shown in FIG. 7, the non-formation area 36 is formed across the entire width of the platen drum 10 in the main scan direction, while is narrower than the width of the pressing surface 32 a in the sub scan direction. A part of the outer circumferential surface 10 b that faces to the pressing surface 32 a composes a part of the formation area 37.

Since the elastic layer 35 is formed as described above, when the clamper 15 is set in the second catching position, the projections 32 b press the sheet front end portion within the non-formation area 36, even if the clamper 15 is in any turn position. Thus, the sheet front end portion makes contact with the metal surface of the platen drum 10, which has the low coefficient of friction, at portions pressed by the projections 32 b, so that the sliding between the sheet front end portion and the outer circumference 10 b is not inhibited. On the other hand, when the clamper 15 is in the first catching position, the pressing surface 32 a tightly presses the sheet front end portion against the elastic layer 35 (formation area 37) having the high coefficient of friction to keep hold of the sheet. This prevents the slip of the sheet 3 during conveyance in printing and the like.

The procedure of detecting skew of the sheet, turning the clamper 15, and the like can be appropriately determined. In this embodiment, the procedure consists of three steps including judgment of an inclination direction, rough adjustment, and fine adjustment. The skew of the sheet 3 is detected, while the sheet 3 is conveyed by the rotation of the platen drum 10. The skew correction is carried out, when the conveyance of the sheet 3 is stopped.

In FIG. 1, the sensor section 8 composes a skew detection section for detecting the skew of the sheet 3 together with the controller 24. The controller 24 judges the inclination direction of the sheet 3 and an inclination angle θ of the sheet 3 based on a detection signal from the sensor section 8, and turns the clamper 15 by controlling the clamper turning mechanism 17 so as to correct the skew. The inclination direction refers to an inclination direction of the lenses 4 in their longitudinal direction with respect to the main scan direction. The inclination angle θ refers to an inclination angle of the lenses 4 in their longitudinal direction with respect to the main scan direction.

The sensor section 8, as shown in FIG. 8, includes first to third lens sensors 41 to 43 that are aligned in the main scan direction. The lens sensors 41 to 43 are disposed so as not to have equal distances therebetween (S1≠S2, S2≠S3, S1≠S3). Each of the lens sensors 41 to 43 is constituted of an LED (light emitting diode) disposed under the sheet 3 and a photosensor disposed oppositely to the LED above the sheet 3. The photosensor receives detection light that has been emitted from the LED and passed through the sheet 3, and outputs a detection signal in accordance with the intensity of the detection light.

For example, the detection signal from each of the lens sensors 41 to 43 gradually increases in a period from when the lens sensor 41 to 43 faces to a boundary between the lenses 4 until when the lens sensor 41 to 43 faces to a vertex of the lens 4, and reaches its peak when the lens sensor 41 to 43 faces to the vertex. After that, the detection signal gradually decreases, and is changed again into the gradual increase when the lens sensor 41 to 43 faces to the boundary between the lenses 4. Note that, in this embodiment, the sensor section 8 also detects the front end of the sheet 3 during feeding, measures the pitch of the lenses 4, and the like.

In the judgment of the inclination direction, a conveyance length LA of the sheet 3 conveyed from the time when the detection signal of the first lens sensor 41 reaches its peak during the conveyance of the sheet 3 to the time when the detection signal of the second lens sensor 42 reaches its peak thereafter is measured. In other words, the conveyance length of the sheet 3 conveyed from the time when the first lens sensor 41 detects the vertex of the arbitrary lens 4 to the time when the second lens sensor 42 detects the vertex of the lens 4 thereafter is measured. Note that, the conveyance length can be obtained based on the number of drive pulses supplied to the motor 14 being a drive source of the platen drum 10, for example, but may be measured using an encoder rotating together with the platen drum 10 or the like.

The distances of the first to third lens sensors 41 to 43 are determined and the large skew of the fed sheet 3 is prevented, such that all of the following conditions are satisfied in a state where the clamper 15 catches the fed sheet 3.

1: When the inclination direction of the sheet 3 is a clockwise direction (C.W. direction of FIG. 8), the first to third lens sensors 41 to 43 detect the vertex of the identical lens 4 in this order.

2: The first to third lens sensors 41 to 43 do not detect the vertexes of the different lenses 4 at the same time.

3: When the inclination angle of the sheet 3 is the clockwise direction, after the first lens sensor 41 detects the vertex of the arbitrary lens 4, the second lens sensor 42 detects the vertex of the identical lens 4.

On the above conditions, the inclination angle θ of the sheet 3 is calculated by the following expression (1) based on the conveyance length LA and the known distance S1 between the first and second lens sensors 41 and 42. The inclination direction of the sheet 3 is assumed to be the clockwise direction. Using the calculated inclination angle θ and the known distance S3 between the first and third lens sensors 41 and 43, a predicted value of a conveyance length LB conveyed to the time when the third lens sensor 43 detects the vertex of the lens 4 identical to the lens 4 that the first lens sensor 41 has detected is calculated by the following expression (2).

θ=tan−1(LA/S1)  (1)

LB=S3×tanθ  (2)

After the calculation of the predicted value of the conveyance length LB, the conveyance length and the detection signal of the third lens sensor 43 from the time when the detection signal of the first lens sensor 41 reaches its peak are monitored, and the inclination direction is judged from the relation therebetween. When the inclination direction of the sheet 3 is the clockwise direction as being assumed, the detection signal of the third lens sensor 43 reaches its peak in the vicinity of a position corresponding to the conveyance length LB. On the other hand, when the inclination direction of the sheet 3 is a counterclockwise direction, the detection signal of the third lens sensor 43 does not reach its peak in the vicinity of the position corresponding to the conveyance length LB. Therefore, in a case where the detection signal of the third lens sensor 43 reaches its peak in the vicinity of the position corresponding to the conveyance length LB, the inclination direction of the sheet 3 is judged to be the clockwise direction. In the other case, the inclination direction of he sheet 3 is judged to be the counterclockwise direction.

The judgment of the counterclockwise direction, as described above, is based on the premise that the above expressions (1) and (2) do not hold when the actual inclination direction of the sheet 3 is the counterclockwise direction. More specifically, when the inclination direction of the sheet 3 is the counterclockwise direction, the conveyance length LA comes to be a length from the time when the first lens sensor 41 detects the vertex of the lens 4 to the time when the second lens sensor 42 detects the vertex of the next lens 4, so the expressions (1) and (2) do not hold.

After the judgment of the inclination direction, the rough adjustment is carried out. When the judged inclination direction of the sheet 3 is the clockwise direction, the inclination angle θ that is calculated in the judgment of the inclination direction from the expression (1) is set at a rough-adjustment inclination angle, and the clamper 15 is turned by the rough-adjustment inclination angle in the counterclockwise direction. Accordingly, the inclination angle θ becomes almost 0°.

On the other hand, when the judged inclination direction of the sheet 3 is the counterclockwise direction, the distance to the peak of the detection signal of the second lens sensor 42 nearest to a criterion, which is the time when the detection signal of the first lens sensor 41 reaches its peak, is calculated as a conveyance length L1. Next, by substituting the conveyance length L1 for the conveyance length LA into the above expression (1), the rough-adjustment inclination angle is obtained. Then, the clamper 15 is turned by the rough-adjustment inclination angle in the clockwise direction.

At this time, when the nearest peak of the detection signal of the second lens sensor 42 is later than the peak of the detection signal of the first lens sensor 41, the nearest peak corresponds to the vertex identical to the vertex of the lens 4 detected before by the first lens sensor 41. Thus, in this case, the calculated rough-adjustment inclination angle is almost equal to the actual inclination angle θ of the sheet 3. On the other hand, when the nearest peak of the detection signal of the second lens sensor 42 is earlier than the peak of the detection signal of the first lens sensor 41, the nearest peak corresponds to the vertex one vertex before the vertex of the lens 4 detected by the first lens sensor 41. Thus, the rough-adjustment inclination angle calculated in this case differs from the actual inclination angle θ, but this presents no problem because the inclination angle θ does not necessarily become 0° in the rough adjustment.

After the rough adjustment, the fine adjustment is carried out. In the fine adjustment, basically as in the case of the calculation of the rough-adjustment inclination angle, a conveyance length L2 to the peak of the detection signal of the third lens sensor 42 nearest to a criterion, which is the peak of the detection signal of the first lens sensor 41, is calculated. Next, by substituting the conveyance length L2 for the conveyance length LA into the above expression (1), a fine-adjustment inclination angle is obtained.

The fine-adjustment inclination angle calculated as described above is equal to the actual inclination angle θ after the rough adjustment. Since the fine adjustment is carried out after the rough adjustment, the inclination angle θ is sufficiently small. Thus, in the fine adjustment, when the inclination direction of the sheet 3 is the counterclockwise direction, the peak of the detection signal of the third lens sensor 43 is later than the peak of the detection signal of the first lens sensor 41. When the inclination direction of the sheet 3 is the clockwise direction, on the contrary, the peak of the detection signal of the third lens sensor 43 is earlier than the peak of the detection signal of the first lens sensor 41. Thus, it is possible to judge the inclination direction from the peaks of the detection signals of the first lens sensor 41 and the third lens sensor 43.

The controller 24 turns the clamper 15 based on the judged inclination direction of the sheet 3 and the calculated fine-adjustment inclination angle so as to make the inclination angle θ of the sheet 3 into 0°. Note that, when the fine-adjustment inclination angle is 0°, it is unnecessary to turn the clamper 15 in the fine adjustment.

In FIG. 9, the clamper shifting mechanism 16 is constituted of movable plates 51 and 52, a cam 53, clutch discs 54 a and 54 b, a motor 55, and the like. On the side of the movable plate 52, another set of the cam 53, the clutch discs 54 a and 54 b, the motor 55, and the like is provided in a like manner, though it is not shown in the drawing.

The movable plates 51 and 52 are attached to side surfaces of the platen drum 10 so as to sandwich the platen drum 10, and are movable in the radial direction. The movable plate 51, 52 is biased downward by a biasing means, for example, springs 60, and makes contact with a cam face of the cam 53 disposed under each movable plate 51, 52. The cam 53 is rotatably attached to each side surface of the platen drum 10.

The clutch disc 54 b on a motor side is movable between a disengaged position away from the clutch disc 54 a on a cam side as shown in the drawing and an engaged position engaged therewith. In the engaged position, the clutch discs 54 a and 54 b transmit rotation without a slip. When the rotation position of the platen drum 10 is set in the standby position, the clutch disc 54 b can be engaged with the clutch disc 54 a. The standby position is a position of waiting for the insertion of the sheet front end portion of the sheet 3 fed from the feeding path 6 into between the platen drum 10 and the clamper 15.

The motors 55 rotate the clutch discs 54 b under control of the controller 24. Thus, the cams 53 are rotated, and the clamper 15 is shifted in the radial direction integrally with the movable plates 51 and 52. In the cam 53, there are formed cam faces 53 a to 53 c, which correspond to the retracted position, the first catching position, and the second catching position of the clamper 15, respectively. By regulating a rotation angle of the cam 53, one of the cam faces 53 a to 53 c comes into contact with the bottom surface of the movable plate 51, 52. Thereby, the clamper 15 is shifted to one of the retracted position, the first catching position, and the second catching position.

Each of the cam faces 53 b and 53 c corresponding to the first and second catching positions is planar, and makes contact with the bottom surface of the movable plate 51, 52 in a state parallel to a direction orthogonal to a moving direction of the movable plate 51, 52. The pair of springs 60 has the same biasing force. Thus, even if the clutch plate 54 b is in the disengaged position, the biasing force of the springs 60 prevents the rotation of the cam 53 pressed by the movable plate 51, 52, and stably holds the clamper 15 in first or second catching position.

Note that, the cam face 53 b corresponding to the first catching position and the cam face 53 c corresponding to the second catching position are joined by a curved surface the diameter of which is equal to or smaller than a distance between the cam face 53 c and the center of the cam 53. Thus, when the clamper 15 is shifted between the first catching position and the second catching position, the clamper 15 is not shifted to the side of the retracted position beyond the second catching position.

The clamper 15 is provided with a shaft 56 at an end on the side of the movable plate 52, and two shafts 57 at the other end on the side of the movable plate 51. The shaft 56 is attached to the movable plate 52 at one end, and is turnable in a turning direction centering on the radial direction of the platen drum 10. The movable plate 51 has a long opening 51 a formed parallel to a tangential direction of the platen drum 10. The shafts 57 extend through the long opening 51 a. Thereby, the clamper 15 is turnable around a turning axis (hereinafter called clamper turning axis) orthogonal to the sheet surface of the sheet 3. In this embodiment, the clamper turning axis passes through an attachment position of the shaft 56 to the movable plate 52, but may pass through a center of the clamper 15 in the width direction, for example.

The clamper turning mechanism 17 is constituted of a mechanism for holding the clamper 15 in a turnable manner, as described above, plates 58 a and 58 b, an actuator 59, and the like. The slide plate 58 a is fixed on ends of the shafts 56 outside the movable plate 51. The slid plate 58 b is shifted between a disengaged position shown in FIG. 9 and an engaged position for tightly contacting with the slide plate 58 a with appropriate pressure. When the platen drum 10 is in the standby position, the slide plate 58 b can tightly come into contact with the slide plate 58 a.

The surface of each slide plate 58 a, 58 b has appropriate elasticity and a high coefficient of friction. In the engaged position, the slide plates 58 a and 58 b slide integrally. Note that, the slide plate 58 b is longer than the slide plate 58 a in a movement direction of the clamper 15. Even if the clamper 15 is in any of the retracted position, the first catching position, and the second catching position, the slide plate 58 b can make tightly contact with the slide plate 58 a.

The actuator 59 slides the slide plate 58 b being in the engaged position under control of the controller 24. Thus, the clamper 15 is turned around the clamper turning axis, to correct the skew of the sheet 3 caught by the clamper 15. This turning operation is carried out in a state of setting the clamper 15 in the second catching position.

When the clamper 15 is turned, the distance between the slide plate 58 a and the end of the clamper 15 is varied. Thus, each of the above shafts 57 is extendable and shortenable. Each shaft is biased by a contained spring, for example, in a direction of shortening its length. Accordingly, the length of the shaft 57 is extended and shortened in accordance with variation of the distance between the slide plate 58 a and the end of the clamper 15. Note that, the shaft 56 may be extended or shortened. Alternatively, a surface of the movable plate 51 and a surface of the slide plate 58 a that make contact with each other may be formed into curved surfaces, so that the distance between the slide plate 58 a and the end of the clamper 15 is not varied.

Note that, when the slide plates 58 a and 58 b are set in the disengaged position, the clamper 15 is not turned around the clamper turning axis due to the friction between the slide plate 58 a and the movable plate 51 and the like. A brake mechanism or the like may be separately provided in order to prevent an unintentional movement or turn of the clamper 15.

As shown in FIG. 1, the rear end clamps 27 are disposed at appropriate distance away from clamper 15 in the circumferential direction of the platen drum 10. The rear end clamps 27 are provided on both of the side surfaces of the platen drum 10, and catch both side edges of the rear end portion of the sheet 3 between themselves and the outer circumferential surface 10 b.

As shown in FIG. 10, the rear end clamp 27 is movable between a catching position in which one end 27 a catches the side edge of the sheet 3 between itself and the platen drum 10 and a release position in which the end 27 a opens outward from the catching position as shown in a chain double-dashed line to release the catch of the sheet 3.

The open/close mechanism 28 for operating the rear end clamp 27 is constituted of a cam 61, clutch discs 62 a and 62 b, a motor 63, and the like. The other end 27 b of the rear end clamp 27 is biased so as to make contact with a cam face of the cam 61, and a sliding position onto the cam face is changed by the rotation of the cam 61, so the rear end clamp 27 is movable between the catching position and the release position.

The clutch disc 62 b on a motor side is disposed in a position slightly advanced from the peeling claw 19 in the rotation direction of the platen drum 10 in printing, in other words, in the forward direction. To operate the rear end clamps 27, the platen drum 10 is rotated to a rotation position (hereinafter called rear end clamp open/close position) in which the clutch disc 62 a is faced to the clutch disc 62 b. The clutch disc 62 b is moved between a disengaged position away from the clutch disc 62 b as shown in the drawing and an engaged position engaged therewith. The motor 63, which is controlled by the controller 24, rotates the cam 53 through the clutch disc 62 b set in the engaged position. Thus, the rear end clamps 27 are set at one of the catching position and the release position.

Next, referring to a flowchart shown in FIG. 11, printing on the lenticular sheet will be described. First, data of the two viewpoint images, in which the same scene is viewed from different viewpoints, is inputted to an input I/F (not shown) of the printer 2. These two viewpoint images are temporarily stored on a memory (not shown) of the controller 24 as the parallax image. A data conversion section provided in the controller 24 reads out the two viewpoint images from the memory, and converts the two viewpoint images into data of six viewpoint images. The data of the six viewpoint images is stored on the memory again.

When the start of printing is directed, the controller 24 confirms that the platen drum 10 is in the standby position and the slide plate 58 b of the clamper turning mechanism 17 is in the disengaged position. Next, the controller 24 engages the clutch disc 54 b with the clutch disc 54 a, and then shifts the clamper 15 to the retracted position by controlling the clamper shifting mechanism 16. Note that, the position of the clamper 15 may be detected by a position sensor or the like, and the clamper shifting mechanism 16 may be controlled based on a detection result. When the clamper 15 is shifted to the retracted position, the rotation position of the clamper 15 may be detected by a rotary encoder or the like, and the clamper turning mechanism 17 maybe controlled based on a detection result so as to parallel the clamper 15 with the main scan direction.

After the clamper 15 is set in the retracted position, the single sheet 3 is fed from the paper feed cassette 9 into the feeding path 6. After that, the sheet 3 is conveyed downward while being nipped by the feeding roller pair 7 rotated by the motor 12. Through this conveyance, the sheet 3 is sent through the sensor section 8 to the platen drum 10. The feeding roller pair 7 conveys the sheet 3 by a certain length from the time when the sensor section 8 detects the front end of the sheet 3. Then, after the sheet front end portion is made ready to be caught by the clamper 15, the rotation of the motor 12 is stopped to halt the conveyance of the sheet 3.

After the conveyance of the sheet 3 is stopped, the controller 24 actuates the clamper shifting mechanism 16 to set the clamper 15 in the first catching position. Thus, the sheet front end portion is caught between the clamper 15 and the outer circumferential surface 10 b of the platen drum 10. At this time, the entire pressing surface 32 a of the pressing member 32 is tightly in contact with the sheet front end portion, because the clamper 15 is in the first catching position.

After the clamper 15 catches the sheet front end portion, the feeding roller pair 7 releases the nip of the sheet 3, and the clutch disc 54 b of the clamper shifting mechanism 16 is moved to the disengaged position. Furthermore, after the thermal head 18 is confirmed to be set in the retracted position, the controller 24 actuates the motor 14. Thereby, the platen drum 10 rotates in the forward direction, and the sheet 3 starts being conveyed in the sub scan direction.

During this conveyance, the controller 24 carries out the judgment of the inclination direction and the calculation of the rough-adjustment inclination angle, based on the detection signals from the lens sensors 41 to 43. As described above, the inclination direction of the lens 4 is judged based on the detection signals from the lens sensors 41 to 43, and the rough-adjustment inclination angle is calculated based on the detection signals of the first and second lens sensors 41 and 42 after the judgment of the inclination direction.

When the judgment of the inclination direction and the calculation of the rough-adjustment inclination angle are completed, the rotation direction of the motor 14 is switched, so the platen drum 10 is reversely rotated and returned to the standby position. At this time, the sheet 3 is conveyed upstream of the feeding path 6.

When the platen drum 10 is stopped in the standby position, the clutch disc 54 b is engaged with the clutch disc 54 a. After that, the clamper shifting mechanism 16 shifts the clamper 15 from the first catching position to the second catching position. At this shift, clamper 15 is directly shifted from the first catching position to the second catching position with preventing the clamper 15 from being set in the retracted position by controlling the rotation direction of the cam 53. Accordingly, the pressing surface 32 a moves away from the sheet 3, and only the projections 32 b press the sheet front end portion.

Subsequently, the slide plate 58 b is moved to the engaged position to be engaged with the slide plate 58 a, and then the clamper turning mechanism 17 turns the clamper 15. At this time, the operation of the actuator 59 is controlled such that the clamper 15 is turned in a direction opposite to the judged inclination direction by the same angle as the rough-adjustment inclination angle.

When the clamper 15 is turned as described above, the sheet 3 is turned together with the clamper 15, and the position of the sheet 3 is changed to roughly adjust the inclination of the lenses 4 in the longitudinal direction relative to the main scan direction. At this time, since the clamper 15 is set in the second catching direction, the sheet front end portion does not slip off from the projections 32 b, but easily slips off from the front surface of the drum body 34. Therefore, the sheet 3 is rotated only by the rough-adjustment inclination angle with precision.

After the completion of the rough adjustment, the slide plate 58 a is set in the disengaged position, and the clamper shifting mechanism 16 shifts the clamper 15 from the second catching position to the first catching position. At this shift, the clamper 15 is directly shifted from the second catching position to the first catching position without being set in the retracted position.

After the clutch disc 54 b is set in the disengaged position, the platen drum 10 is rotated in the forward direction, and the sheet 3 starts to be rotated in the sub scan direction. During the conveyance of the sheet 3, the fine-adjustment inclination angle is calculated based on the detection signals from the first and third lens sensors 41 and 43.

After the calculation of the fine-adjustment inclination angle, the rotation direction of the motor 14 is switched, and the platen drum 10 is reversely rotated and returned to the standby position. When the platen drum 10 is stopped in the standby position, as in the case of the rough adjustment, the clamper shifting mechanism 17 shifts the clamper 15 from the first catching position to the second catching position. After that, the slide plate 58 b is returned to the engaged position, and then the clamper turning mechanism 17 turns the clamper 15 based on a judgment result of the inclination direction and a calculation result of the fine-adjustment inclination angle, so as to parallel the longitudinal direction of the lenses 4 with the main scan direction in the fine adjustment.

After the completion of the fine adjustment, the slide plate 58 b is shifted to the disengaged position, and the clamper shifting mechanism 16 shifts the clamper 15 to the first catching position. After that, the clutch disc 54 b is set in the disengaged position.

After the skew of the sheet 3 is corrected as described above, the sheet 3 is wound onto the platen drum 10. To wind the sheet 3 onto the platen drum 10, the platen drum 10 is rotated forward. By this rotation, the sheet 3 is pulled out of the feeding path 6, and successively wound onto the outer circumferential surface 10 b. During the conveyance of the sheet 3, a lens pitch of the sheet 3 is checked based on a detection result of the sensor section 8. Note that, the lens pitch can be calculated as the conveyance length from the time when the detection signal of the sensor section 8 reaches its peak to the time when the detection signal reaches the next peak, for example.

When even the rear end of the sheet 3 is wound onto the platen drum 10, the rotation of the platen drum 10 is continued until the platen drum 10 arrives at the rear end clamp open/close position. When the platen drum 10 is stopped in the rear end clamp open/close position, the clutch disc 62 b is engaged with the clutch disc 62 a, and the open/close mechanism 28 sets the rear end clamp 27 in the catching position. Thus, the sheet front end portion is clamped by the rear end clamps 27.

The clutch disc 62 b is set in the disengaged position, and the platen drum 10 is rotated forward. When the clamper 15 is moved to a position beyond the thermal head 18, the platen drum 10 is stopped. After the image receptor film of the print film 21 is set directly under the thermal head 18, the thermal head 18 is shifted to the pressing position. Thus, the thermal head 18 presses the image receptor film against the back surface of the sheet 3.

After the press of the thermal head 18, the platen drum 10 is forward rotated again. Thus, the sheet 3 starts to be conveyed in the sub scan direction. The image receptor film is fed in synchronization with the conveyance of the sheet 3. After the start of the conveyance of the sheet 3, the controller 24 monitors the conveyance length of the sheet 3 based on the number of drive pulses supplied to the motor 14. When it is detected that the print area of the sheet 3 arrives at the thermal head 18 by monitoring the conveyance length, the head driver 22 is directed to form the image receptor layer.

The head driver 22 supplies the two heating element arrays 18 a of the thermal head 18 with common electric power to generate heat therein, and heats the image receptor film. Thus, the image receptor film is evenly heated, and the two lines of the transparent image receptor layer extending long in the main scan direction are transferred side by side to the small area 5 a, for example.

After the two lines of the image receptor layer are formed in the small area 5 a, the sheet 3 is conveyed only by a conveyance length corresponding to one-sixth of the lens pitch detected before. This intermittent conveyance amount corresponds to a print width of the single stripe image, and is equal to the width of the small area. Concurrently with this, the image receptor film is shifted by two lines. After the shift, the thermal head 18 is actuated again to heat the image receptor film. Thereby, the image receptor layer is formed in the small area 5 b adjoining to the small area 5 a in which the image receptor layer is formed earlier.

Likewise, with the conveyance of the sheet 3 and the image receptor film, the image receptor layer is formed on a two-line basis, and the transparent image receptor layer is formed in the entire print area in the end.

After the formation of the image receptor layer is completed, the thermal head 18 is returned to the retracted position. The platen drum 10 continues to be rotated forward, and is stopped when the clamper 15 is moved to the position beyond the thermal head 18. After that, the yellow ink film of the print film 21 is set directly under the thermal head 18, and the thermal head 18 is shifted to the pressing position. Thereby, the yellow ink film is overlaid on the back surface of the sheet 3.

After the press of the thermal head 18, the platen drum 10 is rotated forward to convey the sheet 3 again. At this time, the controller 24 monitors the conveyance length of the sheet 3, and when the heating element arrays 18 a of the thermal head 18 are positioned in the first small area 5 a of the print area, two adjoining lines of an yellow image of, for example, the first viewpoint image out of the six viewpoint images is read out. The thermal head 18 is driven based on data of the yellow image. By the heat generation of the two heating element arrays 18 a, the yellow ink film is heated from behind. Thus, yellow ink sublimed from the yellow ink film adheres to the image receptor layer of the small area 5 a. As a result, the single stripe image consisting of the two lines of the yellow image is printed on the small area 5 a.

After the print on the small area 5 a, the sheet 3 is conveyed by the rotation of the platen drum 10 only by the conveyance length corresponding to one-sixth of the lens pitch. Concurrently with the conveyance of the sheet 3, the yellow ink film is wound up such that an unused portion thereof is faced to the thermal head 18 instead of a used portion. After the conveyance, two adjoining lines of yellow image data of the second viewpoint image are read out, and the head driver 22 makes the two heating element arrays 18 a generate heat in accordance with the yellow image data, so the stripe image consisting of the two lines of the yellow image is printed on the small area 5 b.

Likewise, whenever the sheet 3 and the yellow ink film are conveyed by the conveyance length corresponding to one-sixth of the lens pitch, the thermal head 18 is actuated based on the two lines of the yellow image data, to print the stripe images of the first to sixth viewpoint images on the small areas 5 a to 5 f, respectively.

When the yellow images are completely printed on the entire print area of the sheet 3, the thermal head 18 is shifted to the retracted position. The platen drum 10 continues to be rotated forward, and is stopped in a position where the clamper 15 passes by the thermal head 18. Then, the print film 21 is fed so as to set the magenta ink film directly under the thermal head 18. After that, the thermal head 18 is shifted to the pressing position.

As in the case of the yellow images described above, while the sheet 3 and the magenta ink film are conveyed intermittently, each magenta image of the first to sixth viewpoint images is split into stripe images, and the stripe images are printed on the back surface of the sheet 3 so as to be overlaid on the stripe images of the yellow images. After a single screen of the magenta images is completely printed, cyan images are printed on the sheet 3 using the cyan ink film.

After the cyan images are printed, the thermal head 18 is shifted to the retracted position. The platen drum 10 continues to be rotated to a position where the clamper 15 passes by the thermal head 18, and is stopped. After that, the back layer film of the print film 21 is set directly under the thermal head 18, and then the thermal head 18 is shifted to the pressing position. While the sheet 3 is intermittently conveyed again by the forward rotation of the platen drum 10, the thermal head 18 is actuated to form the back layer on the print area on which the images of three colors have already been printed.

After the formation of the back layer, the thermal head 18 is shifted to the retracted position. The platen drum 10 is forward rotated a little, and stopped in the rear end clamp open/close position. After the platen drum 10 is stopped, the clutch disc 62 b is shifted to the engaged position, and then the rear end clamps 27 are moved to the release position by the open/close mechanisms 28. The peeling claw 19 is swung to the peeling position in which the peeling claw 19 is in contact with the outer circumferential surface 10 b.

After that, the platen drum 10 is rotated reversely. When the rear end of the sheet 3 arrives at the position of the peeling claw 19 by this reverse rotation, the peeling claw 19 scoops up the rear end of the sheet 3 from the outer circumferential surface 10 b. The platen drum 10 continues to be rotated reversely, so the sheet 3 is guided to the cutter unit 25 from its rear end.

When the platen drum 10 arrives at the standby position by the reverse rotation, the reverse rotation of the platen drum 10 is temporarily stopped. At this time, the sheet 3 fed into the cutter unit 25 has reached a constant length, and the conveyance mechanism of the cutter unit 25 can convey the sheet 3.

When the platen drum 10 is stopped in the standby position, as described above, the clamper shifting mechanism 16 shifts the clamper 15 to the retracted position. After that, since the conveyance mechanism of the cutter unit 25 conveys the sheet 3, the front end of the sheet 3 is pulled out from between the clamper 15 and the platen drum 10, and the entire sheet 3 is conveyed to the cutter unit 25. In the cutter unit 25, the sheet front end portion and the sheet rear end portion being margins in which no image is printed are cut off, and the remaining sheet 3 is ejected. In the case of carrying out printing on another sheet 3, the above procedure is repeated.

In the above embodiment, the non-formation area in which no elastic layer is formed has a rectangular shape with appropriate widths in the main scan direction and the sub scan direction, but may be in another shape as long as the non-formation area is formed in the outer circumferential surface of the platen drum at least at areas facing to the projections and shiftable areas of the projections by the turning mechanism. In an embodiment shown in FIG. 12, non-formation areas 36 a and 36 b are formed only in portions at which projections 32 b tightly make contact with the sheet 3 plus surroundings of the portions. In correcting the skew of the sheet 3, since the clamper 15 is turned and the projections 32 b are shifted, the non-formation areas 36 a and 36 b are formed in the shiftable areas of the projections 32 b. Note that, in this embodiment of FIG. 12, the non-formation area 36 b on the side of the shaft 56 is small, while the non-formation area 36 a on the side of the shaft 57 is large, considering the fact that the clamper pivots on the shaft 56.

The projections provided in the pressing member 32 may be different in size from each other. In an embodiment shown in FIG. 13, a projection 71 on a pivot side of the clamper 15 that is moved a little relative to the other is made small, while a projection 72 on the opposite of the pivot side that is moved much is made large to increase the size of a contact area with the sheet 3. Note that, the number of the projections provided in the pressing member of the clamper 15 may be three or more.

In each of the above embodiments, the printer of a platen drum type having the platen drum as the support member is described, but a flat platen table that moves integrally with the clamper or the like may be used, instead of the platen drum. In another case, the fixed platen table or a platen roller with a small diameter may be disposed in a position facing to the thermal head. The thermal head may be pressed against the sheet on the platen table or the platen roller for printing, while the sheet may be caught between the clamper and the support member provided separately from the platen table, and the support member and the clamper may be integrally moved in the sub scan direction to convey the sheet.

In each of the above embodiments, the line printer is described, but the present invention is applicable to a printer of another type, such as a serial printer. Furthermore, the present invention is applicable not only to the printing of the parallax image for recording the 3D image, but also to the printing of so-called changing, in which a viewable image is changed with a change of an observation position. The present invention is usable in a thermal fusion type of thermal printer, an inkjet printer, and the like, in addition to a sublimation type.

Furthermore, the printer is described above, but the clamping device according to the present invention is also applicable to various types of equipment that require switching between a skew correction state and a sheet fixing state, other than the printer. For example, the present invention is applicable to a cutting device that cuts the lenticular sheet into appropriate size in such a manner that its cutting direction is orthogonal or parallel to the longitudinal direction of the lenses. In this cutting device, the lenticular sheet on the support member is pressed and caught by the clamper. To correct the skew of the lenticular sheet relative to a cutting blade, the clamper is set in the second catching position and turned. When cutting the lenticular sheet, the clamper is set in the first catching position to prevent a slip of the lenticular sheet. The present invention is usable to the case of not conveying the sheet, as a matter of course.

The clamping device catches the lenticular sheet at any portion as long as it does not interfere with a process to be carried out while catching the lenticular sheet, such as printing of an image, cutting, and the like. In the printer, the lenticular sheet can be caught at any portion on which no image is printed, and the portion preferably could be a sheet end portion including the sheet front end portion, the sheet rear end portion, side end portions, and the like. In the case of cutting out the lenticular sheet into constant size, the lenticular sheet can be caught at its middle portion.

DESCRIPTION OF THE REFERENCE NUMERALS

2 printer

3 lenticular sheet

4 lens

8 sensor section

10 platen drum

15 clamper

16 clamper shifting mechanism

17 clamper turning mechanism

18 thermal head

24 controller

32 pressing member

32 a pressing surface

32 b projection 

1. A clamping device comprising: a clamper having a pressing member with elasticity, for catching a part of a lenticular sheet between said pressing member and a support member for supporting at least a part of said lenticular sheet; a clamper shifting mechanism for shifting said damper among a retracted position, a first catching position, and a second catching position, said pressing member being away from said support member in said retracted position, said pressing member pressing said part of said lenticular sheet so as to prevent a slip of said lenticular sheet from said pressing member and said support member in said first catching position, said pressing member pressing said part of said lenticular sheet so as to prevent a slip of said lenticular sheet from said pressing member and allow a slip of said lenticular sheet from said support member in said second catching position; a clamper turning mechanism for turning said clamper around a turning axis orthogonal to said lenticular sheet; and a controller, wherein when turning said lenticular sheet being caught, said controller controls said clamper shifting mechanism and said clamper turning mechanism so as to set said clamper in said second catching position and turn said clamper; when fixing said lenticular sheet on said support member, said controller controls said clamper shifting mechanism so as to set said clamper in said first catching position.
 2. The clamping device as recited in claim 1, wherein said pressing member has a plurality of projections formed in a pressing surface faced to said support member; said first catching position denotes a position in which said pressing surface is pressed against said part of said lenticular sheet while compressing each of said projections, to catch said part of said lenticular sheet between said pressing surface and said support member; and said second catching position denotes a position in which each of said projections is pressed against said part of said lenticular sheet with a compression value of each of said projections lower than that of said first catching position, to catch said part of said lenticular sheet between each of said projections and said support member.
 3. The clamping device as recited in claim 2, wherein a size of said projection is in accordance with a distance from said turning axis, and in said second catching position, an area at which said projection contacts with said lenticular sheet differs in accordance with said distance from said turning axis.
 4. The clamping device as recited in claim 2, wherein out of a surface area of said support member, at least an area faced to said projection plus a movable area of said projection by said clamper turning mechanism are allocated to a non-formation area, and a remaining area is allocated to a formation area, and an elastic layer having elasticity is formed in said formation area to make a coefficient of friction in said non-formation area smaller than that in said formation area.
 5. The clamping device as recited in claim 4, wherein said formation area includes a portion of said support member faced to said pressing surface, such that said part of said lenticular sheet is caught between said pressing surface and said elastic layer when said damper is in said first catching position.
 6. A printer having a printing section that conveys in a sub scan direction a lenticular sheet having a plurality of lenses formed in a front surface of said lenticular sheet, and sequentially prints on a back surface of said lenticular sheet a plurality of stripe images parallel to a main scan direction orthogonal to said sub scan direction, said printer comprising: a platen for supporting said lenticular sheet and moving said lenticular sheet in said sub scan direction; a clamper having a pressing member with elasticity, for pressing a sheet end portion of said lenticular sheet against said platen to catch said sheet end portion between said clamper itself and said platen; a clamper shifting mechanism for shifting said clamper among a retracted position, a first catching position, and a second catching position, said pressing member being away from said platen in said retracted position, said pressing member pressing said sheet end portion so as to prevent a slip of said lenticular sheet from said pressing member and said platen in said first catching position, said pressing member pressing said sheet end portion so as to prevent a slip of said lenticular sheet from said pressing member and allow a slip of said lenticular sheet from said platen in said second catching position; a skew detection section for detecting skew of said lenticular sheet; a damper turning mechanism for turning said clamper around a turning axis orthogonal to said lenticular sheet; and a controller, wherein when correcting said skew of said lenticular sheet with respect to said main scan direction, said controller controls said damper shifting mechanism and said clamper turning mechanism to set said clamper in said second catching position and turn said clamper based on a detection result of said skew detection section; and when conveying said lenticular sheet in said sub scan direction, said controller controls said clamper shifting mechanism to set said clamper in said first catching position while said platen is moved in said sub scan direction.
 7. The printer as recited in claim 6, wherein said pressing member has a plurality of projections formed in a pressing surface faced to said platen; said first catching position denotes a position in which said pressing surface is pressed against said sheet end portion while compressing each of said projections, to catch said sheet end portion between said pressing surface and said platen: and said second catching position denotes a position in which each of said projections is pressed against said sheet end portion with a compression value of each of said projections lower than that of said first catching position, to catch said sheet end portion between each of said projections and said platen.
 8. The printer as recited in claim 7, wherein a size of said projection is in accordance with a distance from said turning axis, and in said second catching position, an area at which said projection contacts with said sheet end portion differs in accordance with said distance from said turning axis.
 9. The printer as recited in claim 7, wherein out of a surface area of said platen, at least an area faced to said projection plus a movable area of said projection by said clamper turning mechanism are allocated to a non-formation area, and a remaining area is allocated to a formation area, and an elastic layer having elasticity is formed in said formation area, and a coefficient of friction is smaller in said non-formation area than that in said formation area.
 10. The printer as recited in claim 9, wherein said formation area includes a portion of said platen faced to said pressing surface, such that said sheet end portion is caught between said pressing surface and said elastic layer when said clamper is in said first catching position.
 11. The printer as recited in claim 6, wherein said platen comprises a rotatable platen drum on which said lenticular sheet is wound.
 12. The printer as recited in claim 6, wherein a sheet front end portion of said lenticular sheet is caught between said clamper and said platen.
 13. The clamping device as recited in claim 3, wherein out of a surface area of said support member, at least an area faced to said projection plus a movable area of said projection by said clamper turning mechanism are allocated to a non-formation area, and a remaining area is allocated to a formation area, and an elastic layer having elasticity is formed in said formation area to make a coefficient of friction in said non-formation area smaller than that in said formation area.
 14. The printer as recited in claim 8, wherein out of a surface area of said platen, at least an area faced to said projection plus a movable area of said projection by said damper turning mechanism are allocated to a non-formation area, and a remaining area is allocated to a formation area, and an elastic layer having elasticity is formed in said formation area, and a coefficient of friction is smaller in said non-formation area than that in said formation area.
 15. The printer as recited in claim
 7. wherein said platen comprises a rotatable platen drum on which said lenticular sheet is wound.
 16. The printer as recited in claim 8, wherein said platen comprises a rotatable platen drum on which said lenticular sheet is wound.
 17. The printer as recited in claim 9, wherein said platen comprises a rotatable platen drum on which said lenticular sheet is wound.
 18. The printer as recited in claim 10, wherein said platen comprises a rotatable platen drum on which said lenticular sheet is wound.
 19. The printer as recited in claim 2, wherein a sheet front end portion of said lenticular sheet is caught between said clamper and said platen.
 20. The printer as recited in claim 3, wherein a sheet front end portion of said lenticular sheet is caught between said clamper and said platen. 